Introduction: The Work Productivity and Activity Impairment (WPAI) questionnaire is a well validated instrument to measure impairments in work and activities. However, its validation among patients with rheumatoid arthritis (RA) has not been well established. The present study's purpose is to evaluate the construct validity of the WPAI-general health version among RA patients and its ability to differentiate between RA patients with varying health status.
Methods: Patients who were enrolled in the Early Rheumatoid Arthritis Network cohort and were employed at their most recent follow-up were recruited into this sub-study. A questionnaire battery incorporating the WPAI was administered along with a number of health outcomes including the Multidimensional Health Assessment Questionnaire, fatigue and patient assessment of disease activity. The construct validity of the WPAI was tested by the correlations between the WPAI and the health outcomes and other measures of productivity. Student's t tests were used to identify whether the WPAI outcomes differed between the two levels of heath status based on the median of health outcomes.
Results: A total of 150 patients completed the WPAI questionnaire. The average age was 52 years old and the disease duration was 37.5 months since the first rheumatology visit. Of the 137 patients who were working for pay, 26 reported missing work in the past week due to their health problem, accounting for 45.5% of their working time (absenteeism). While 123 patients were working, 24% of their work was impaired due to their health problem (presenteeism). In addition, 33% of the patients' regular daily activities (activity impairment) had been prevented due to their health problems. There were moderate correlations between the WPAI absenteeism and function, pain, fatigue, and disease severity (r = 0.34 to 0.39). The WPAI presenteeism and activity impairment were strongly correlated with the health outcomes (0.67 to 0.77). Patients with more severe disease status (for example, low/high functional disability by median) had significantly higher absenteeism (4%/15%), presenteeism (15%/39%), and activity impairment (19%/53%) than those with less severe disease status.
Conclusions: The WPAI is a valid questionnaire for assessing impairments in paid work and activities in RA patients and for measuring the relative differences between RA patients with different health status.